Method of passivating of low dielectric materials in wafer processing

ABSTRACT

A method of passivating silicon-oxide based low-k materials using a supercritical carbon dioxide passivating solution comprising a silylating agent is disclosed. The silylating agent is preferably an organosilicon compound comprising organo-groups with five carbon atoms such as hexamethyldisilazane (HMDS) and chlorotrimethylsilane (TMCS) and combinations thereof. The silicon oxide-based low-k material, in accordance with embodiments of the invention, is maintained at temperatures in a range of 40 to 200 degrees Celsius, and preferably at a temperature of about 150 degrees Celsius, and at pressures in a range of 1,070 to 9,000 psi, and preferably at a pressure of about 3,000 psi, while being exposed to the supercritical passivating solution. In accordance with further embodiments of the invention, a silicon oxide-based low-k material is simultaneously cleaned and passivated using a supercritical carbon dioxide cleaning solution.

RELATED APPLICATION(S)

[0001] This Patent Application claims priority under 35 U.S.C. 119 (e)of the co-pending U.S. Provisional Patent Application Serial No.60/361,917 filed Mar. 4, 2002, and entitled “METHODS OF PASSIVATINGPOROUS LOW-K DIELECTRIC FILM” and the co-pending U.S. Provisional PatentApplication Serial No. 60/369,052 filed Mar. 29, 2002, and entitled “USEOF SUPERCRITICAL CO² PROCESSING FOR INTEGRATION AND FORMATION OF ULKDIELECTRICS”. The Provisional Patent Application Serial No. 60/361,917filed Mar. 4, 2002, and entitled “METHODS OF PASSIVATING POROUS LOW-KDIELECTRIC FILM” and the Provisional Patent Application Serial No.60/369,052 filed Mar. 29, 2002, and entitled “USE OF SUPERCRITICAL CO₂PROCESSING FOR INTEGRATION AND FORMATION OF ULK DIELECTRICS” are alsoboth hereby incorporated by reference.

FIELD OF THE INVENTION

[0002] The present invention relates to the field of micro-deviceprocessing. More particularly, the present invention relates topassivating low dielectric materials with supercritical processingsolutions.

BACKGROUND OF THE INVENTION

[0003] Semiconductor fabrication generally uses photoresist in etchingand other processing steps. In the etching steps, a photoresist masksareas of the semiconductor substrate that are not etched. Examples ofthe other processing steps include using a photoresist to mask areas ofa semiconductor substrate in an ion implantation step or using thephotoresist as a blanket protective coating of a processed wafer orusing the photoresist as a blanket protective coating of a MEMS (microelectromechanical system) device. State of the art integrated circuitscan contain up to 6 million transistors and more than 800 meters ofwiring. There is a constant push to increase the number of transistorson wafer-based integrated circuits. As the number of transistors isincreased there is a need to reduce the cross-talk between the closelypacked wire in order to maintain high performance requirements. Thesemiconductor industry is continuously looking for new processes and newmaterials that can help improve the performance of wafer-basedintegrated circuits.

[0004] Materials exhibiting low dielectric constants of between 3.5-2.5are generally referred to as low-k materials and porous materials withdielectric constant of 2.5 and below are generally referred to as ultralow-k (ULK) materials. For the purpose of this application low-kmaterials refer to both low-k and ultra low-k materials. Low-k materialshave been shown to reduce cross-talk and provide a transition into thefabrication of even smaller integrated circuit geometries. Low-kmaterials have also proven useful for low temperature processing. Forexample, spin-on-glass materials (SOG) and polymers can be coated onto asubstrate and treated or cured with relatively low temperature to makeporous silicon oxide-based low-k layers. Silicon oxide-based herein doesnot strictly refer silicon-oxide materials. In fact there are a numberof low-k materials which have silicon oxide and hydrocarbon componentsand/or carbon, wherein the formula is SiO_(x)C_(x)H_(z), referred toherein as hybrid materials and designated herein as MSQ materials. It isnoted, however, that MSQ is often designated to mean MethylSilsesquioxane, which is an example of the hybrid low-k materialsdescribed above. Some low-k materials such as carbon doped oxide (COD)or fluoridated silicon glass (FSG), are deposited using chemical vapordeposition techniques, while other low-k materials, such as MSQ,porous-MSQ, and porous silica, are deposited using a spin-on process.

[0005] While low-k materials are promising materials for fabrication ofadvanced micro circuitry, they also provide several challenges they tendbe less robust that more traditional dielectric layer and can be damagedby etch and plasma ashing process generally used in pattern dielectriclayer in wafer processing, especially in the case of the hybrid low-kmaterials, such as described above. Further, silicon oxide-based low-kmaterials tend to be highly reactive after patterning steps. Thehydrophillic surface of the silicon oxide-based low-k material canreadily absorb water and/or react with other vapors and/or processcontaminants which can alter the electrical properties of the dielectriclayer itself and/or diminish the ability to further process the wafer.

[0006] What is needed is a method of passivating a low-k layerespecially after a patterning steps. Preferably, the method ofpassivating the low-k layer is compatible with other wafer processingsteps, such as processing steps for removing contaminants and/orpost-etch residue after a patterning step.

SUMMARY OF THE INVENTION

[0007] The present invention is directed to passivating silicon-oxidebased low-k materials using a supercritical passivating solution. Low-kmaterials are usually porous oxide-based materials and can include anorganic or hydrocarbon component. Examples of low-k materials include,but are not limited to, carbon-doped oxide (COD), spin-on-glass (SOG)and fluoridated silicon glass (FSG) materials. In accordance with theembodiments of the present invention, a supercritical passivatingsolution comprises supercritical carbon dioxide and an amount of apassivating agent that is preferably a silylating agent. The silylatingagent can be introduced into supercritical carbon dioxide neat or with acarrier solvent, such as N, -dimethylacetamide (DMAC),gamma-butyrolacetone (BLO), dimethyl sulfoxide (DMSO), ethylenecarbonate (EC) N-methylpyrrolidone (NMP), dimethylpiperidone, propylenecarbonate, alcohol or combinations thereof, to generate thesupercritical passivating solution. In accordance with a preferredembodiment of the invention, the silylating agent is an organosiliconcompound, and silyl groups (Si(CR₃)₃) attack silanol (Si—OH) groups onthe surface of the silicon oxide-based low-k dielectric material and/orin the bulk of the silicon oxide-based low-k dielectric material to formsurface capped organo-silyl groups during the passivating step.

[0008] In accordance with further embodiments of the invention, asilicon oxide-based low-k material is passivated with a supercriticalpassivating solution comprising supercritical carbon dioxide and anorganosilicon compound that comprises organo-groups with 5 carbon atomsor fewer. In accordance with a preferred embodiment of the invention theorgano-groups, or a portion thereof, are methyl groups. For example,suitable organosilicon compounds useful as silylating agents in thepresent invention include, but are not limited to, hexamethyldisilazane(HMDS) and chlorotrimethylsilane (TMCS), trichloromethylsilane (TCMS)and combinations thereof. Alternatively, a source of (CH₃) radicals canbe used to as a silylating agent.

[0009] During a supercritical passivating step, a silicon oxide-basedlow-k material, in accordance with the embodiments of the invention, ismaintained at temperatures in a range of 40 to 200 degrees Celsius, andpreferably at a temperature of approximately 150 degrees Celsius, and atpressures in a range of 1,070 to 9,000 psi, and preferably at a pressureof approximately 3,000 psi, while a supercritical passivating solution,such as described above, is circulated over the surface of the siliconoxide-based low-k material.

[0010] In accordance with still further embodiments of the invention,the surface of the silicon oxide-based low-k material is dried orretreated prior to the passivating step. In accordance with thisembodiment of the invention, the silicon oxide-based low-k material isdried, or retreated by exposing the low-k materials to a supercriticalsolution of supercritical carbon dioxide or supercritical carbon dioxidewith one or more solvents including but not limited to ethanol,methanol, n-hexane and combinations thereof.

[0011] While a supercritical processing solution with methanol andethanol primarily remove water from low-k materials, a supercritcialprocessing solution with n-hexane is believed to remove hydroxyl groupsfrom low-k materials and facilitate the ability of a silylating agent,or agents, to silylate the low-k materials in the passivation processingstep.

[0012] In accordance with yet further embodiments of the invention, adielectric surface is passivated during a cleaning processing step,wherein a post-etch residue is simultaneously removed from thedielectric surface using a supercritical cleaning solution comprising apassivating agent, such as described above. The post-etch residue caninclude a photoresist polymer or a photoresist polymer with ananti-reflective dye and/or an anti-reflective layer.

[0013] In accordance with the method of the present invention, apatterned low-k dielectric layer is formed by depositing a continuouslayer of a low-k dielectric material, etching a pattern in the low-kmaterial and removing post-etch residue using a supercritical solutioncomprising supercritical carbon dioxide and a silicon-based passivatingagent.

[0014] After a low-k material is patterned by treating the low-kmaterial to an etch and/or ash process, the low-k material can show amarked increase in the k-values as a result of degeneration of thematerial and/or removal of a portion of the organic component, in thecase of low-k hybrid materials; increases in k-values that are greaterthan 1.0 have been observed. The method of passivation, in accordancewith the present invention has the ability to restore or recover aportion of the of the k-value lost in the patterning steps. In fact ithas been observed that low-k materials passivated, in accordance withthe embodiments of the present invention can be restored to exhibitk-values near, or at, k-values of the original and un-patternedmaterial.

[0015] Further details of supercritical systems suitable for treatingwafer substrates to supercritical processing solutions are furtherdescribed in U.S. patent application Ser. No. 09/389,788, filed Sep. 3,1999, and entitled “REMOVAL OF PHOTORESIST AND PHOTORESIST RESIDUE FROMSEMICONDUCTORS USING

[0016] SUPERCRITICAL CARBON DIOXIDE PROCESS” and U.S. patent applicationSer. No. 09/697,222, filed Oct. 25, 2000, and entitled “REMOVAL OFPHOTORESIST AND RESIDUE FROM SUBSTRATE USING SUPERCRITICAL CARBONDIOXIDE PROCESS”, both of which are hereby incorporated by reference.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] FIGS. 1A-C show schematic representations of organosiliconstructures used as silylating agents in a supercritical processing step,in accordance with the embodiments of the invention.

[0018]FIGS. 1D shows schematic representations of silylating agentsreacting with silanol groups in a low-k material, in accordance with theembodiments of the invention.

[0019]FIG. 1E illustrates steric hindrance between a silanol-group and asilyl-group on a surfaces of a low-k material, which can lead toincomplete silylating of the surface.

[0020]FIG. 2 shows a simplified schematic of a supercritical waferprocessing apparatus, in accordance with the embodiments of theinvention.

[0021]FIG. 3 shows a detailed schematic diagram of a supercriticalprocessing apparatus, in accordance with the embodiments of theinvention.

[0022]FIG. 4 is a plot of pressure versus time for a supercriticalcleaning, rinse or curing processing step, in accordance with the methodof the present invention.

[0023]FIG. 5 is a schematic block diagram outlining steps for treating asilicon oxide-based low-k layer, in accordance with the embodiments ofthe present invention.

[0024]FIG. 6 shows infrared absorption spectra for a silicon-based low-kmaterial before and after treatment with a passivating agent, inaccordance with embodiments of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0025] In semiconductor fabrication, a dielectric layer is generallypatterned using a photoresist mask in one or more etching and ashingsteps. Generally, to obtain the high resolution line widths and highfeature aspect ratios, an anti-reflective coating is required. Inearlier processes, anti-reflective coating (ARC) of titanium nitride(TiN) were vapor deposited on the dielectric layer and the TiNanti-reflective coatings would not be removed after patterning butrather remain a part of the device fabricated. With new classes of lowdielectric layers that can be made to be very thin, TiN anti-reflectivecoatings are not preferred because anti-reflective coatings can dominateover the electrical properties of the dielectric layer. Accordingly,polymeric spin-on anti-reflective coatings with an anti-reflective dyethat can be removed after a patterning step are preferred. Regardless ofthe materials that are used in the patterning steps, after patterningthe dielectric layer these materials are preferably removed from thedialectic layer after the patterning process is complete.

[0026] Porous low-k materials are most commonly silicon-oxide based withsilanol (Si—OH) groups and/or organo components as described above.These low-k materials can become activated and/or damaged, which isbelieved to be in-part is due to depletion of an organic componentduring etch and/or ash steps. In either case of activation and/ordamage, additional silanol groups are exposed which can readily adsorbwater and/or contaminants and/or chemicals that are present during otherprocessing steps. Accordingly, partial device structures with exposedlow-k dielectric layers are difficult to handle and maintain contaminantfree, especially after patterning steps. Further, activation and/ordamage the bulk of the low-k material can result in increased k-values.It has been observed low-k materials that are activated and/or damagedcan exhibit increases in k-values by 1.0 or more.

[0027] The present invention is directed to a method of and system forpassivating porous low-k dielectric materials. The method of the presentinvention preferably passivates a layer of patterned low-k layer byend-capping silanol groups on the surface and/or in the bulk of thelow-k material to produce a patterned low-k material which is morehydrophobic, more resistant to contamination and/or less reactive. Inaccordance with the embodiments of the present invention, a passivationprocessing step is carried out separately from a supercritical post-etchcleaning process or, alternatively, is carried out simultaneously with asupercritical post-etch cleaning process.

[0028] Referring now to FIG. 1A, in accordance with the embodiments ofthe invention, a supercritical passivating solution comprises a silanestructure 10 which can have all organo groups, such as in the case withhexamethyldisilazane (HMDS) or a combination of organo and halide groups(F, Cl, Br and etc.) which are attached to any one of the positions 1-4.

[0029] Now referring to FIG. 1B, in accordance with further embodimentsof the invention, a supercritical passivating solution comprises apent-valent organosilicon compound 20, wherein the silicon atom iscoordinated to 5 ligands in the positions 1, 2, 3, 4 and 5 in atiganolbipyramidal configuration. Typically such compounds 20 are anionswith one or more of the positions 1-5 being coordinated with halideatom, such as in the case with a difluorotrimethylilicate anion. Whenthe structure 20 is an anion, the compound 20 also includes a suitablecation, such as sodium, potassium or any other inorganic or organiccation (not shown).

[0030] Now referring FIG. 1C, in accordance with yet further embodimentsof the present invention, a supercritical passivating solution comprisesa silazane structure 30, which can be described as an amine structurewith two organosilyl groups coordinated to the nitrogen of the amine,such as in the case of hexamethyldisilazane (HMDS).

[0031]FIGS. 1D shows schematic representations of hexamethyldisilazane(HMDS) reacting with silanol groups on a surface of a low-k material inreaction sequence (1) and trimethyldisilazane (TMDS) reacting withsilanol groups on a surface of the low-k material in reaction sequence(2). Note that trimethyldisilazane (TMDS) is a product in the reactionsequence (1), which can then further react with silanol groups on asurface of the low-k material in accordance with reaction sequence (2).Hence, hexamethyldisilazane (HMDS) provides is a excellent silylatingagent for use in accordance with the method of the present invention.

[0032]FIG. 1E illustrates steric hindrance between a silanol group 53and silyl-group 55 on a surface 51 of a low-k material. Note that thesilanol group 53 is extremely large and can actually provide aprotective barrier for the silanol group 53. Accordingly, it is notgeneral possible to completely silylate an entire surface or bulk of alow-k material.

[0033] However, when the low-k material is pre-treated with asupercritical processing solution comprising supercritical carbondioxide and n-hexane, it is believed that a greater percent of thesilanol groups 53 are replace with silyl-groups 55 on the surface 51. Itwill be clear to one skilled in the art that a supercritical passivatingsolution with any number of silylating agents and combinations ofsilylating agents are within the scope of the present invention.Further, the silylating agent or agents used can be can be introducedinto supercritical carbon dioxide neat or along with a carrier solvent,such as N, N-dimethylacetamide (DMAC), gamma-butyrolacetone (BLO),dimethyl sulfoxide (DMSO), ethylene carbonate (EC) N-methylpyrrolidone(NMP), dimethylpiperidone, propylene carbonate, alcohol or combinationsthereof to generate the supercritical passivating solution. Also, asexplained previously the passivating agent or agents used in the presentinvention can be used in supercritical cleaning processes to removepost-etch residues from a surface of a patterned low-k material.

[0034] The present invention is particularly well suited for removingpost-etch photopolymer from a wafer material and even more specificallyis well suited to remove a post-etch photopolymer and/or a polymericanti-reflective coating layer from a low-k silicon oxide-based layer,including low-k layers formed from porous MSQ and porous SiO₂ (e.g.,Honeywell's NANOGLASS®), while simultaneously passivating a siliconoxide-based layer. For the purpose of simplicity, supercriticalprocessing solutions are referred to herein as either a supercriticalcleaning and/or a supercritical passivating solution.

[0035]FIG. 2 shows a simplified schematic of a supercritical processingapparatus 200.

[0036] The apparatus 200 comprises a carbon dioxide source 221 that isconnected to an inlet line 226 through a source valve 223 which can beopened and closed to start and stop the flow of carbon dioxide form thecarbon dioxide source 221 to the inlet line 226. The inlet line 226 ispreferably equipped with one or more back-flow valves, pumps andheaters, schematically shown by the box 220, for generating and/ormaintaining a stream of supercritical carbon dioxide. The inlet line 226also preferably has a inlet valve 225 that is configured to open andclose to allow or prevent the stream of supercritical carbon dioxidefrom flowing into a processing chamber 201.

[0037] Still referring to FIG. 2, the process camber 201 is preferablyequipped with one or more pressure valves 209 for exhausting theprocessing chamber 201 and/or for regulating the pressure within theprocessing chamber 201. Also, the processing chamber 201, in accordancewith the embodiments of the invention is coupled to a pump and/or avacuum 211 for pressurizing and/or evacuating the processing chamber201.

[0038] Again referring to FIG. 2, within the processing chamber 201 ofthe apparatus 200 there is preferably a chuck 233 for holding an/orsupporting a wafer structure 213.

[0039] The chuck 233 and/or the processing chamber 201, in accordancewith further the embodiments of the invention, has one or more heaters231 for regulating the temperature of the wafer structure 213 and/or thetemperature of a supercritical processing solution within the processingchamber 201.

[0040] The apparatus 200, also preferably has a circulation line or loop203 that is coupled to the processing chamber 201. The circulation line203 is preferably equipped with one or more valves 215 and 215′ forregulating the flow of a supercritical processing solution through thecirculation line 203 and through the processing chamber 201. Thecirculation line 203, is also preferably equipped with any numberback-flow valves, pumps and/or heaters, schematically represent by thebox 205, for maintaining a supercritical processing solution and flowingthe supercritical process solution through the circulation line 203 andthrough the processing chamber 201. In accordance with a preferredembodiment of the invention, the circulation line 203 has an injectionport 207 for introducing chemistry, such as a passivating agents andsolvents, into the circulation line 203 for generating supercriticalprocessing solutions in situ.

[0041]FIG. 3 shows a supercritical processing apparatus 76 in moredetail than FIG. 2 described above. The supercritical processingapparatus 76 is configured for generating and for treating a wafer withsupercritical cleaning, rinse and curing solutions. The supercriticalprocessing apparatus 76 includes a carbon dioxide supply vessel 332, acarbon dioxide pump 334, the processing chamber 336, a chemical supplyvessel 338, a circulation pump 340, and an exhaust gas collection vessel344. The carbon dioxide supply vessel 332 is coupled to the processingchamber 336 via the carbon dioxide pump 334 and carbon dioxide piping346. The carbon dioxide piping 346 includes a carbon dioxide heater 348located between the carbon dioxide pump 334 and the processing chamber336. The processing chamber 336 includes a processing chamber heater350. The circulation pump 340 is located on a circulation line 352,which couples to the processing chamber 336 at a circulation inlet 354and at a circulation outlet 356. The chemical supply vessel 338 iscoupled to the circulation line 352 via a chemical supply line 358,which includes a first injection pump 359. A rinse agent supply vessel360 is coupled to the circulation line 352 via a rinse supply line 362,which includes a second injection pump 363. The exhaust gas collectionvessel 344 is coupled to the processing chamber 336 via exhaust gaspiping 364.

[0042] The carbon dioxide supply vessel 332, the carbon dioxide pump334, and the carbon dioxide heater 348 form a carbon dioxide supplyarrangement 349. The chemical supply vessel 338, the first injectionpump 359, the rinse agent supply vessel 360, and the second injectionpump 363 form a chemical and rinse agent supply arrangement 365.

[0043] It will be readily apparent to one skilled in the art that thesupercritical processing apparatus 76 includes valving, controlelectronics, filters, and utility hookups which are typical ofsupercritical fluid processing systems.

[0044] Still referring to FIG. 3, in operation a wafer (not shown) witha residue thereon is inserted into the wafer cavity 312 of theprocessing chamber 336 and the processing chamber 336 is sealed byclosing the gate valve 306. The processing chamber 336 is pressurized bythe carbon dioxide pump 334 with the carbon dioxide from the carbondioxide supply vessel 332 and the carbon dioxide is heated by the carbondioxide heater 348 while the processing chamber 336 is heated by theprocessing chamber heater 350 to ensure that a temperature of the carbondioxide in the processing chamber 336 is above a critical temperature.The critical temperature for the carbon dioxide is 31° C. Preferably,the temperature of the carbon dioxide in the processing chamber 336 iswithin a range of range of from 40° C. to about 200° C., and preferablyat or near to 150° C., during a supercritical passivating step.

[0045] Upon reaching initial supercritical conditions, the firstinjection pump 359 pumps the processing chemistry, such as a silylatingagent, from the chemical supply vessel 338 into the processing chamber336 via the circulation line 352 while the carbon dioxide pump furtherpressurizes the supercritical carbon dioxide. At the beginning of theaddition of processing chemistry to the processing chamber 336, thepressure in the processing chamber 336 is preferably about 1,070 to9,000 psi and preferably at or near 3,000 psi. Once a desired amount ofthe processing chemistry has been pumped into the processing chamber 336and desired supercritical conditions are reached, the carbon dioxidepump 334 stops pressurizing the processing chamber 336, the firstinjection pump 359 stops pumping processing chemistry into theprocessing chamber 336, and the circulation pump 340 begins circulatingthe supercritical cleaning solution comprising the supercritical carbondioxide and the processing chemistry. Preferably, the pressure withinthe processing chamber 336 at this point is about 3000 psi. Bycirculating the supercritical processing solution, supercriticalprocessing solution is replenished quicky at the surface of the waferthereby enhancing the rate of passivating the surface of a low-kdielectric layer on a wafer.

[0046] When a wafer (not shown) with a low-k layer is being processedwithin the pressure chamber 336, the wafer is held using a mechanicalchuck, a vacuum chuck or other suitable holding or securing means. Inaccordance with the embodiments of the invention the wafer is stationarywithin the processing chamber 336 or, alternatively, is rotated, spun orotherwise agitated during the supercritical process step.

[0047] After the supercritical processing solution is circulated thoughcirculation line 352 and the processing chamber 336, the processingchamber 336 is partially depressurized by exhausting some of thesupercritical process solution to the exhaust gas collection vessel 344in order to return conditions in the processing chamber 336 to near theinitial supercritical conditions. Preferably, the processing chamber 336is cycled through at least one such decompression and compression cyclebefore the supercritical processing solutions are completely exhaustingthe processing chamber 336 to the exhaust into the collection vessel344. After exhausting the pressure chamber 336 a second supercriticalprocess step is performed or the wafer is removed from the processingchamber 336 through the gate valve 306, and the wafer processingcontinued second processing apparatus or module (not shown).

[0048]FIG. 4 illustrates an exemplary plot 400 of pressure versus timefor a supercritical process step, such as a supercriticalcleaning/passivating process step, in accordance with the method of thepresent invention. Now referring to both FIGS. 3 and 4, prior to aninitial time T₀, the wafer structure with post-etch residue thereon isplaced within the processing chamber 336 through the gate valve 306 andthe processing chamber 336 is sealed. From the initial time T₀ through afirst duration of time T₁, the processing chamber 336 is pressurized.When the processing chamber 336 reached critical pressure P_(c) (1,070psi) then a processing chemistry including a silylating agents isinjected into the processing chamber 236, preferably through thecirculation line 352, as explained previously. The processing chemistrypreferably includes hexamethyldisilazane (HMDS), chlorotrimethylsilane(TMCS), trichloromethylsilane (TMCS) and combinations thereof which areinjected into the system. Several injections of process chemistries canbe performed over the duration of time T₁ to generate a supercriticalprocessing solution with the desired concentrations of chemicals. Theprocessing chemistry, in accordance with the embodiments of theinvention, can also include one more or more carrier solvents, amminesalts, hydrogen fluoride and/or other sources of fluoride. Preferably,the injection(s) of the process chemistries begin upon reaching about1100-1200 psi, as indicated by the inflection pint 405. Alternatively,the processing chemistry is injected into the processing chamber 336around the second time T₂ or after the second time T₂.

[0049] After processing chamber 336 reaches an operating pressure P_(op)at the second time T₂ which is preferably about 3,000 psi, but can beany value so long as the operating pressure is sufficient to maintainsupercritical conditions, the supercritical processing solution iscirculated over and/or around the wafer and through the processingchamber 336 using the circulation line 325, such as described above.Then the pressure within the processing chamber 336 is increases andover the duration of time the supercritical processing solutioncontinues to be circulated over and/or around the wafer and through theprocessing chamber 336 using the circulation line 325 and or theconcentration of the supercritical processing solution within theprocessing chamber is adjusted by a push through process, as describedbelow.

[0050] Still referring to FIG. 4, in a push-through process, over theduration of time T₃ a fresh stock of supercritical carbon dioxide fedinto the processing chamber 336, while the supercritical cleansingsolution along with process residue suspended or dissolved therein issimultaneously displaced from the processing chamber 336 through thevent line 364. After the push-through step is complete, then over aduration of time T₄, the processing chamber 336 is cycled through aplurality of decompression and compression cycles. Preferably, this isaccomplished by venting the processing chamber 336 below the operatingpressure POP to about 1,100-1,200 psi in a first exhaust and thenraising the pressure within the processing chamber 336 from 1,100-1,200psi to the operating pressure POP or above with a first pressurerecharge. After, the decompression and compression cycles are complete,then the processing chamber is completely vented or exhausted toatmospheric pressure. For wafer processing, a next wafer processing stepbegins or the wafer is removed form the processing chamber and moved toa second process apparatus or module to continue processing.

[0051] The plot 400 is provided for exemplary purposes only. It will beunderstood by those skilled in the art that a supercritical processingstep can have any number of different time/pressures or temperatureprofiles without departing from the scope of the present invention.Further any number of cleaning and rinse processing sequences with eachstep having any number of compression and decompression cycles arecontemplated.

[0052] Also, as stated previously, concentrations of various chemicalsand species withing a supercritical processing solution can be readilytailored for the application at hand and altered at any time within asupercritical processing step. In accordance with the preferredembodiment of the invention, a low-k layer is treated to 1 to 10passivation steps in approximately 3 minute cycles, as described abovewith reference to FIGS. 3-4.

[0053]FIG. 5 is a block diagram 500 outlining steps for treating asubstrate structure comprising a patterned low-k layer and post-etchresidue thereon using a supercritical cleaning and passivating solution.In the step 502 the substrate structure comprising the post-etch residueis placed and sealed within a processing chamber. After the substratestructure is placed into and sealed within processing chamber in thestep 502, in the step 504 the processing chamber is pressurized withsupercritical CO₂ and processing chemistry is added to the supercriticalCO₂ to generate a supercritical cleaning and passivating solution.Preferably, the cleaning and passivating chemistry comprises at leastone organosilicon compound.

[0054] After the supercritical cleaning and passivating solution isgenerated in the step 504, in the step 506 the substrate structure ismaintained in the supercritical processing solution for a period of timesufficient to remove at least a portion of the residue from thesubstrate structure and passivate surfaces exposed after the reside isremoved. During the step 506, the supercritical cleaning and passivatingsolution is preferably circulated through the processing chamber and/orotherwise agitated to move the supercritical cleaning solution oversurfaces of the substrate structure.

[0055] Still referring to FIG. 5, after at least a portion of theresidue is removed from the substrate structure in the step 506, theprocessing chamber is partially exhausted in the step 508. The cleaningprocess comprising steps 504 and 506 are repeated any number of times,as indicated by the arrow connecting the steps 508 to 504, required toremove the residue from the substrate structure and passivate thesurfaces exposed. The processing comprising steps 504 and 506, inaccordance with the embodiments of the invention, use freshsupercritical carbon dioxide, fresh chemistry or both. Alternatively,the concentration of the cleaning chemistry is modified by diluting theprocessing chamber with supercritical carbon dioxide, by addingadditional charges of cleaning chemistry or a combination thereof.

[0056] Still referring to FIG. 5, after the processing steps 504, 506and 508 are complete, in the step 510 the substrate structure ispreferably treated to a supercritical rinse solution. The supercriticalrinse solution preferably comprises supercritical CO₂ and one or moreorganic solvents, but can be pure supercritical CO₂.

[0057] Still referring to FIG. 5, after the substrate structure iscleaned in the steps 504, 506 and 508 and rinsed in the step 510, in thestep 512 the processing chamber is depressurized and the substratestructure is removed from the processing chamber.

[0058] Alternatively, the substrate structure is cycled through one ormore additional cleaning/rinse processes comprising the steps 504, 506,508 and 510 as indicated by the arrow connecting steps 510 and 504.Alternatively, or in addition to cycling the substrate structure throughone or more additional cleaning/rinse cycles, the substrate structure istreated to several rinse cycles prior to removing the substratestructure from the chamber in the step 512, as indicated by the arrowconnecting the steps 510 and 508.

[0059] As described previously, the substrate structure can be driedand/or pretreated prior to passivating the low-k layer thereon by usinga supercritical solution comprising supercritical carbon dioxide and oneor more solvents such as methanol, ethanol, n-hexane and/or combinationthereof. Also, as mentioned previously pretreating the low-k layer withsupercritical solution comprising supercritical carbon dioxide andn-hexane appears to improve the coverage of the silyl-groups on surfaceof the low-k layer. Also, it will be clear of one skilled in the artthat a wafer comprising a post-etch residue and/or a patterned low-kdialectic layer can be treated to any number cleaning and passivatingsteps and/or sequences.

[0060] It will be understood by one skilled in the art, that while themethod of passiavting low-k material has been primarily described hereinwith reference to a post-etch treatment and/or a post-etch cleaningtreatment, the method of the present invention can be used to directlypassivate low-k materials. Further, it will be appreciated that whentreating a low-k material, in accordance with the method of the presentinvention, a supercritical rinse step is not always necessary and simplydrying the low-k material prior treating the low-k material with asupercritical passivating solution can appropriate for someapplications.

EXPERIMENTAL RESULTS

[0061] Using a supercritical processing system, such as described indetail above in reference to FIGS. 2 and 3, samples with a low-k layerformed form MSQ materials were treated with a silylating agent underseveral conditions. Under a first set of conditions, a sample with alayer of the low-k layer material was treated with a solution of hexaneand approximately 6 percent TMCS. The sample was then annealed atapproximately 100° C. for approximately 1.0 hr. Under a second set ofconditions a sample with a layer of the low-k material was treated witha supercritical carbon dioxide passivating solution with approximately1.0 percent TMCS at approximately 3,000 psi.

[0062] Under yet a third set of conditions, a sample with a layer of thelow-k material was treated with a supercritical dioxide passivatingsolution with approximately 1.0 percent TMCS at approximately 3,000 psiat 100° C. After treatment of the samples under the conditions describedabove, Fourier Transform Infrared Spectra of an untreated samples andeach of the treated sample were collected. A comparative plot of theFourier Transform Infrared Spectra collected are shown in FIGS. 6A-B.

[0063]FIG. 6A plots the infrared spectra region from approximately 0 to4,000 wave numbers. The peak 611 corresponds to the C—H stretching ofthe Si(CH₃)₃ groups, which has considerably increased for all of thesamples treated with the silylating agent. The peak 661 corresponds toC—H bending of the Si(CH₃)₃ groups, which has also considerablyincreased for all of the samples treated with the silylating agent. FIG.6B shows comparative plots of an expanded region of the infrared spectrashown in FIG. 6A, from approximately 2,800 wave numbers to 3,100 wavenumbers to more clearly illustrate the increase in the peak 661 for thetreated samples.

[0064] Still referring to FIG. 6A, the a broad peak 663 corresponding toO—H stretching, which is negligible in the in the treated samples, butis pronounced in the untreated sample. From spectra shown in FIGS. 6A-B,it is clear that TMCS is an effective silylating agent for thepassivation of low-k material surfaces in both wet bench conditions andunder supercritical processing conditions.

[0065] The present invention has the advantages of being capable ofpassivating a low-k surface and being compatible with other processingsteps, such as removing post-etch residues (including, but not limitedto, spin-on polymeric anti-reflective coating layers and photopolymers)for patterned low-k layers in a supercritical processing environment.The present invention also has been observed restore or partiallyrestore k values of materials lost after patterning steps and has beenshown to produce low-k layers that are stable over time.

[0066] While the present invention has been described in terms ofspecific embodiments incorporating details to facilitate theunderstanding of the principles of construction and operation of theinvention, such references herein to specific embodiments and detailsthereof is not intended to limit the scope of the claims appendedhereto. It will be apparent to those skilled in the art thatmodifications may be made in the embodiments chosen for illustrationwithout departing from the spirit and scope of the invention.Specifically, while supercritical CO₂ is the preferred medium forcleaning, other supercritical media alone or in combination withsupercritical CO₂ and combinations of hydrogen fluoride adducts arecontemplated.

What is claimed is:
 1. A method of treating a low-k surface comprising:a treating the low-k surface to a supercritical passivating solutioncomprising supercritical CO₂ and an amount of a silylating agentcomprising organic groups; and b. removing the supercritical solution,wherein the low-k surface is at least partially passivated with theorganic groups.
 2. The method of claim 1, wherein the organic groupscomprise alky groups.
 3. The method of claim 1, wherein the organicgroups comprise 5 carbon atoms or fewer. 4 The method of claim 1,wherein the organosilicon compound is selected from the group consistingof hexamethyldisilazane (HMDS), chlorotrimethylsilane (TMCS) andtrichloromethylsilane (TCMS).
 5. The method of claim 1, wherein thesupercritical passivating solution further comprises a carrier solvent.6. The method of claim 5, wherein the carrier solvent is selected fromthe group consisting of N, N-dimethylacetamide (DMAC),gamma-butyrolacetone (BLO), dimethyl sulfoxide (DMSO), ethylenecarbonate (EC), N-methylpyrrolidone (NMP), dimethylpiperidone, propylenecarbonate and alcohol.
 7. The method of claim 1, wherein the low-ksurface is maintained at temperatures in a range of 40 to 200 degreesCelsius.
 8. The method of claim 1, wherein treating the low-k surface toa supercritical passivating solution comprises circulating thesupercritical passivating solution over the low-k surface.
 9. The methodof claim 1, wherein the supercritical passivating solution is maintainedat pressures in a range of 1,000 to 9,000 psi.
 10. The method of claim1, further comprising drying the low-k surface prior to treating thelow-k surface to a supercritical solution.
 11. The method of claim 10,wherein drying the low-k surface comprises treating the low-k surface toa supercritical drying solution comprising supercritical carbon dioxide.12. The method of claim 1, wherein the low-k surface comprisessilicon-oxide.
 13. The method of claim 1, wherein the low-k surfacecomprises a material selected from the group consisting of a carbondoped oxide (COD), a spin-on-glass (SOG) and fluoridated silicon glass(FSG).
 14. A method of treating a dielectric surface, comprising: a)removing post etch residue from the dielectric surface with asupercritical cleaning solution; and b) treating the dielectric surfacewith a passivating agent in the supercritical cleaning solution to forma passivated dielectric surface.
 15. The method of claim 14, wherein theresidue comprises a polymer.
 16. The method of claim 15, wherein thepolymer is a photoresist polymer.
 17. The method of claim 16, whereinthe photoresist polymer comprises an anti-reflective dye.
 18. The methodof claim 14, wherein the dielectric surface comprises silicon oxide. 19.The method of claim 14, wherein the dielectric surface comprises amaterial selected from the group consisting of a carbon doped oxide(COD), a spin-on-glass (SOG) and fluoridated silicon glass (FSG). 20.The method of claim 14, wherein the post etch residue comprises anantireflective coating.
 21. The method of claim 20, wherein theanti-reflective coating comprises an organic spin-on anti-reflectivematerial.
 22. The method of claim 14, wherein the passivating agentcomprises an organosilicon compound.
 23. The method of claim 22, whereinthe organosilicon compound is selected from the group consisting ofhexamethyldisilazane (HMDS) and chlorotrimethylsilane (TMCS) andtrichloromethylsilane (TCMS)
 24. A method of forming a patterned low-kdielectric layer, the method comprising; a. depositing a continuouslayer of low-k dielectric material; b. forming a photoresist mask overthe continuous layer of low-k dielectric material; c. patterning thecontinuous layer of low-k dielectric material through the photoresistmask, thereby forming a post-etch residue; and d. removing the post-etchresidue using a supercritical solution comprising supercritical carbondioxide and a silicon-based passivating agent.
 25. The method of claim24, wherein the supercritical processing solution comprisessupercritical carbon dioxide.
 26. The method of claim 24, wherein thesilicon-based passivating agent comprises an organosilicon compound. 27.A method of forming dielectric layer with a reduced k-value, the methodcomprising a. patterning the layer of dielectric material to form apatterned dielectric layer with a k-value; and d. passivating thepatterned dielectric layer with a k-value with passivating agent to formthe patterned low-k dielectric layer with the reduced k-value.
 28. Themethod of claim 27, wherein the k-value is greater than 3.0.
 29. Themethod of claim 28, wherein the reduced k-value is less that 3.0
 30. Themethod of claim 29, wherein k-value and the reduced k-value differ by1.0 or more.
 31. The method of claim 27, therein the dielectric materialcomprises a silicon-oxide component and hydrocarbon component.
 32. Themethod of claim 31, wherein the passivating agent is a silylating agentcomprising organic groups.